Fluid powered expansion engine

ABSTRACT

A pair of similar free piston mechanisms oscillate, in response to a driving fluid, within respective multi-chambered cavities of a pair of cross coupled cylinder structures. They travel at the same speed but one-fourth of a cycle out of phase. Each pistoncylinder system is double acting and provides the necessary intake and exhaust valving for the other. No mechanical interconnections are needed between the two piston mechanisms. In the disclosed embodiment the expansion engine is incorporated in a fluid transformer having a primary flow circuit, which includes chambers of both cavities, and a secondary flow circuit also comprising chambers of both cavities. Driving fluid in the primary circuit actuates both of the piston mechanisms and they in turn effect pumping of a driven fluid through the secondary circuit.

United States Patent 1 3,711,224 Jan. 16, 1973 Maudlin [54] FLUID POWERED EXPANSION ENGINE [75] lnventor: Wendell E. Maudlin, York, Pa.

[73] Assignee: Borg-Warner Corporation, Chicago,

Ill.

[22] Filed: Feb. 16, 1971 [21] Appl. No.: 115,507

Primary Examiner-Robert M. Walker Attorney-Donald W. Banner, William S. McCurry and John W. Butcher [57] ABSTRACT A pair of similar free piston mechanisms oscillate, in response to a driving fluid, within respective multichambered cavities of a pair of cross coupled cylinder structures. They travel at the same speed but onefourth of a cycle out of phase. Each piston-cylinder system is double acting and provides the necessary intake and exhaust valving for the other. No mechanical interconnections are needed between the two piston mechanisms. In the disclosed embodiment the expansion engine is incorporated in a fluid transformer having a primary flow circuit, which includes chambers of both cavities, and a secondary flow circuit also comprising chambers of both cavities. Driving fluid in the both of the piston mechanisms and they in turn effect pumping of a 19 Claims, 5 Drawing Figures [52] US. Cl. ..4l7/344 [51] Int. Cl. ..F04b 17/00, F04b 35/00 [58] Field of Search ..417/344, 345, 346

[56] References Cited UNITED STATES PATENTS 2,442,916 6/1948 Buchanan ..417/346 2,858,767 11/1958 Smith i ..4l7/346 primary circuit actuates 2,942,553 6/1960 Moeller et al. ...4l7/344 X 3,363,575 1/1968 Potts ..417 344 driven fl id through the Secondary circuit, 3,597,116 8/1971 Tilney ..4l7/344 Secondary ln let 7 wmnlllll lll, nun

E Secondary Oulle'r w I YAWIIAIUIIIIIIII.

Primory Outlet TIIIIIIII4 Primary Inlet PATENIEDJAH 16 Ian 3. 71 1; 224

sum 1 OF 3 goocoumm A In FLUID POWERED EXPANSION ENGINE BACKGROUND OF THE INVENTION This invention relates to a novel fluid-powered expansion engine useful in widely diverse fields. It is particularly attractive when employed in a fluid transformer, and will be described in that environment.

Expansion engines, suitable for commercial applications, are relatively complex and expensive, usually requiring many moving parts, valves, rods, springs, etc. Moreover, previously developed expansion engines have not been susceptible for use in fluid transformers. Applicants expansion engine, on the other hand, is of relatively simple construction, involving only two moving parts, and represents a substantial cost savings over those developed heretofore. In addition, the unique expansion engine of the invention readily lends itself to incorporation in a fluid transformer.

It is, therefore, an object of the invention to provide a new and improved fluid-powered expansion engine.

Another object is to provide an expansion engine of comparatively simple and economical construction.

A further object of the invention is to provide an expansion engine adaptable to a broad range of applications, and particularly adaptable for use in a fluid transformer.

Another goal is to provide a new and improved fluid transformer.

SUMMARY OF THE INVENTION The fluid-powered expansion engine of the invention is driven by driving fluid which is received at an inlet at a predetermined drive pressure and is discharged at an outlet at a lower exhaust pressure. The engine comprises first and second cylinder structures respectively having first and second cavities each of which includes at least one cylindrical chamber. There are first and second free piston mechanisms respectively movable through the first and second cavities. Means, including at least a portion of the second piston mechanism, provides intake and exhaust valving of the first cavity to effect, in response to the driving fluid, double acting reciprocating or oscillating movement of the first piston mechanism through a two-stroke cycle. The engine also comprises means, which includes at least part of the first piston mechanism, for providing intake and exhaust valving of the second cavity to cause, in response to the driving fluid, double acting reciprocating movement of the second piston mechanism through a two-stroke cycle.

In accordance with another aspect of the invention, a pump may be driven by the first and second piston mechanisms to pump a driven fluid through a flow circuit different than that through which the driving fluid passes.

DESCRIPTION OF THE DRAWINGS The features of the invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood, however, by reference to the following description in conjunction with the accompanying drawings in which like reference numbers identify like elements, and in which:

FIGS. 1 and 2 each depicts the detailed construction of a fluid transformer incorporating an expansion engine embodying the invention; together those figures show the transformers operating cycle at four different steps one quarter of a cycle apart;

FIG. 3 is a schematic representation of a refrigeration system, specifically an air conditioning system, and illustrates one particular use to which the fluid transformer of FIGS. 1 and 2 may be applied; and,

FIGS. 4 and 5 are pressure-enthalpy diagrams helpful in explaining the operation of the refrigeration system.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Before considering the illustrated fluid transform er in detail, it will be advantageous to initially review the basic characteristics and function of a transformer of the fluid type. Briefly, such a transformer is a piston-actuated device having two isolated but interdependent flow circuits, the fluid (liquid or gas) passing through one of them (called the primary) normally controlling or driving the fluid in the other or secondary circuit. The primary will serve as the prime mover in the transformer so long as the pressure of the fluid at the inlet to the primary is greater than that of the fluid at the outlet. This means that the fluid expands as it flows through the primary. The pressure differential across the primary circuit in combination with the flow rate, namely the volume of fluid flowing through the primary per unit of time, produce energy which in turn is transmitted to the secondary flow circuit in the form of compression work to achieve pumping of the fluid through the secondary, the fluid compressing in the secondary and thus having a pressure at the secondary outlet that is higher than its pressure at the secondary inlet.

The fluid transformer of the invention comprises two similar fluid actuated piston systems operating at the same speed (the transformers operating speed) but one-fourth of a cycle out of phase, each piston system automatically providing the intake and exhaust porting for the other. Collectively FIGS. 1 and 2 depict the transformer at four different steps of its operating cycle, the steps being spaced apart by one-fourth of a cycle. More particularly, the transformer has a pair of cylinder structures 22 and 24 shown for convenience of illustration as two separate structures. Preferably, in practice structures 22 and 24 would be integrally related to each other in one composite cylinder block. Each structure is hollowed out to form a single large cavity which is effectively divided into five smaller cylindrical chambers having parallel axes. To explain, the cavity in structure 22 includes the large centrally located cylindrical chamber 26, the two small cylindrical chambers 27 and 28 on the right, and the two small cylindrical chambers 31 and 32 on the left, all four of chambers 27, 28, 31 and 32 having the identical crosssectional area. In like fashion, cylinder structure 24 is also hollowed out to provide a single large cavity containing the five smaller cylindrical chambers 34, 35, 36, 37 and 38.

The primary inlet couples to both chambers 31 and 36 via ports 39 and 41 respectively. The primary outlet communicates with chambers 32 and 35 by way of ports 42 and 43 respectively. Chambers 31 and 32 are interconnected via port 44, while chambers 35 and 36 communicate through port 45. The secondary inlet connects to two different sections of chamber 38 by means of ports 46 and 47, and communicates through ports 48 and 49 to two different points along chamber 27. The secondary outlet is connected via ports 51 and 52 to two different sections of chamber 37 and through ports 53 and 54 to two different parts of chamber 28. Chambers 27 and 28 are coupled together through port 55, while chambers 37 and 38 are interconnected via port 56. Chambers 31 and 38 are cross coupled through ports 57 and 58 and the line or conduit connected therebetween. Similarly, ports 58 and 59 and the intermediate fluid line permits cross coupling of chambers 28 and 35.

In addition, chamber 26 is connected to chambers 37 and 38 and chamber 34 connects to chambers 27 and 28. These interconnections are made by means of a series of ports whose axes are perpendicular to the crosssectional view shown in each of FIGS. 1 and 2; consequently those ports are illustrated in circular configuration. Each cylinder structure 22 and 24 has eight such ports designated by the reference numbers 61-68. They have been given the same reference numerals in both cylinder structures since each pair of cor- 'respondingly numbered ports actually constitutes only a single port. As mentioned, structures 22 and 24 preferably would be constructed as a single composite cylinder block. By forming the cylinder block so that structures 22 and 24 are effectively back-to-back, port 61 of structure 22 may be aligned and made coincident with port 61 of structure 24, while at the same time each of the other seven pairs of correspondingly numbered ports may likewise be aligned and made coincident. Hence, in reality there need be only a total of eight ports in the compositetcylinder block.

Reciprocally movable through the large cavity of each structure 22, 24, and through a two-stroke cycle, is an associated free piston mechanism which comprises five separate cylindrical pistons all mechanically fixed to each other, each movable within a respective one of the five chambers of the cavity. Specifically, free piston mechanism 70 has five different portions 71-75 forming separate pistons sized for movement within respective ones of chambers 26, 31, 32, 27 and 28. Piston 72 is further divided into a full diameter portion 72a to provide a land for blocking port 57, a reduced diameter portion 720 for intercoupling ports 57 and 44, and a full diameter portion 72b. Piston 74 is broken up into three full diameter portions 74a, 74b and 740, with a pair of intermediate reduced diameter portions 74d and 74e, portion 74b providing lands for closing ports 48, 49, 65 and 67, portion 74d effecting intercoupling of ports 48 and 65, and portion 74e facilitating intercoupling of ports 49 and 67. Piston 75 has a pair of full diameter portions 75a and 75b between which is a reduced diameter portion 750, portion 75a causing blocking of ports 53 and 66, portion 750 effecting intercoupling of ports 53 and 66 and also of ports 54 and 68.

In like manner free piston mechanism 80, whose shape is similar to that of piston mechanism 70, combines five different pistons 81-85 each of which is reciprocally movable within respective ones of chambers 34, 35, 36, 37 and 38. Piston 82 has a pair of full diameter portions 82a and 82b separated by a reduced diameter portion 82c. Piston 84 is divided into three full diameter portions 84a, 84b and 84c and a pair of reduced diameter portions 84d and 84e. Piston 85 has full diameter portions 85a and 85b and an intermediate reduced diameter portion 85c. The various portions of pistons 82, 84 and 85 effect opening and closing of ports in structure 24 in the same manner as described above in connection with piston mechanism 70.

Of course, in a practical construction of the fluid transformer several piston rings would be employed. They are especially desirable since both the primary and secondary fluid flow through different parts of each of the two cavities and it is important to isolate the primary and secondary flow circuits so that there is no leakage where they interface. The piston rings have not been illustrated in order to avoid encumbering the drawings.

The fluid transformer has two different operating modes; in one the nominal primary drives the nominal secondary and in the other mode the secondary powers the primary. In the first mentioned mode the primary effectively functions as a fluid actuated expansion engine and the secondary acts as a fluid pump, driving fluid supplied to the primary inlet powering each of free piston mechanisms 70, 80 through its two-stroke cycle and fluid supplied to the secondary inlet serving as the driven or pumped fluid. In the latter mode of operation the functions are reversed, the secondary then constituting a fluid-powered expansion engine. In effect, there are actually two expansion engines in the transformer; one is in the primary and the other is in the secondary and each is constructed in accordance with the invention.

The operation of the transformer will initially be described when functioning in its first mode at which time the primary circuit serves as the prime mover and the fluid delivered to the primary inlet has a higher pressure than that at the primary outlet. For convenience, the pressure of the fluid at the primary inlet may be referred to as the drive pressure, while the lower pressure at which the fluid is discharged at the primary outlet may be called the exhaust pressure. In FIG. 1 piston mechanism is shown in full line construction halfway through one of its strokes and moving to the right as indicated by arrow 91. Piston mechanism lags mechanism 70 by one quarter of a cycle so it is shown in full line construction in FIG. 1 in its extreme position on the left and starting to move to the right as indicated by arrow 92. For convenience, mechanism 70 may be referred to as the leading piston mechanism and mechanism 80 as the lagging piston mechanism. Each of the piston mechanisms is also shown in FIG. 1 in dashed construction one fourth of a cycle later, mechanism 70 therefore being at its rightmost position while mechanism 80 is midway through its travel or stroke and heading toward the right. One quarter of a cycle still later mechanism 70 is half way through its other stroke and moving to the left as shown in full line construction in FIG. 2 and as is indicated by arrow 93. At that same time mechanism 80, lagging by one fourth of a cycle, will be established at its rightmost position, as shown in full line construction in FIG. 2, and will be starting to move to the left as indicated by arrow 94. Finally, one fourth of a cycle later mechanism 70 will be at its extreme left position while mechanism 80 will be centered and traveling to the left, as illustrated by the dashed forms of the piston mechanisms in FIG. 2. Piston mechanisms 70 and 80, one quarter of a cycle subsequently, will return to their positions shown in full line construction in FIG. 1.

The manner in which the piston mechanisms are cyclically actuated through the illustrated positions in response to fluid flowing in the primary circuit will now be described. Movement of each of the piston mechanisms to the right is effected by establishing the fluid at the left end or side of the mechanism at the higher drive pressure, while at the same time the fluid at the right end is established at the much lower exhaust pressure. Conversely, movement of each piston mechanism to the left is caused by establishing the fluid on the right side at the drive pressure and the fluid on the left side at the exhaust pressure. The two ends of each piston mechanism are alternately established at drive and exhaust pressures by valving controlled by the other piston mechanism. As will be made apparent the primary flow circuit of the fluid transformer may be thought of as comprising means, which includes a portion of piston mechanism 80, for providing intake and exhaust valving of the large cavity in cylinder structure 22 to effect, in response to the driving fluid, double acting reciprocating movement of piston mechanism 70 through its two-stroke cycle. In addition, the primary circuit may be considered as also comprising means, which includes a portion of piston mechanism 70, for providing intake and exhaust valving of the large cavity in cylinder structure 24 to effect, in response to the driving fluid, double acting reciprocating movement of piston mechanism 80 through its two-stroke cycle.

To explain, consider initially the action of the fluid transformer as piston mechanisms 70 and 80 travel between their positions shown in FIG. 1, namely as mechanism 70 moves from its center to its rightmost position while mechanism 80 shifts from its leftmost to its center position. During that quarter of a cycle, the driving fluid flows from the primary inlet through port 39 and into chamber 31 and thence through port 57 (the land provided by the full diameter portion 720 will be moving to the right) to chambers 37 and 38, those chambers being intercoupled via port 56 throughout the entire cycle. The left ends of pistons 72, 84 and 85 will therefore be established at the drive pressure. Meanwhile, chambers 27 and 28 (intercoupled via port 55 at all times) are coupled through ports 58 and 59,

chamber 35 and port 43 to the primary outlet. Hence, the right ends of pistons 74, 75 and 82 will all be at the lower exhaust pressure. It is also to be noted that chamber 36 communicates through port 41 to the primary inlet while chamber 32 couples through port 42 to the primary outlet. The net pressure at the left end of each piston mechanism, however, will be the drive pressure while the net pressure on their right ends will be the exhaust pressure.

For a complete understanding of the operation, it is necessary to consider the volume of fluid flowing at any given instant into the primary inlet and also out of the primary outlet. It will be assumed that the primary fluid is liquid refrigerant. As the piston mechanisms are traveling to the right and through their quarter cycles shown in FIG. 1, the volume of liquid flowing into chamber 31 per unit of time may be designated AV. Since all eight of the small pistons have the identical cross sectional area, each of chambers 37 and 38 effectively displaces liquid in the amount AV from the primary inlet and through ports 39, 57 and 58. Hence, a total of three AV is being drawn from the primary inlet by chambers 31, 37 and 38. As piston 73 moves to the right liquid in the amount AV is being sucked or robbed from the discharge or primary outlet. As a result, a net amount of 3 AV is being drawn from the primary inlet at the left side of the fluid transformer and 1 AV is being robbed from the discharge. On the right side of the transformer, each of pistons 74, 75 and 82 is pumping or pushing liquid in the amount AV toward the primary outlet. Since piston 83is moving to the right, and thus working against the primary inlet, the net effect on the right side of the transformer is to deliver the amount 3 AV to the outlet and 1 AV to the inlet. As a consequence, by combining the left and right ends at any given instant the same amount of fluid (2 AV) is being sucked in from the primary inlet as is being discharged out at the primary outlet.

When leading mechanism reaches its extreme right position its motion will be reversed by valving controlled by mechanism 80. Since lagging mechanism 80 will now be centered but still traveling to the right, the land provided by full diameter portion 82a momentarily blocks port 59 (as shown in dashed construction in FIG. 1) to disconnect chambers 27 and 28 from the discharge outlet. As mechanism 80 continues its rightward movement chambers 27 and 28 will communicate with the primary inlet via ports 58, 59, 45 and 41, chamber 36 and the annular portion of chamber 35 surrounding reduced diameter section 820. The right ends of both pistons 74 and 75 will thus be established at the drive pressure to propel mechanism 70 to the left. Driving fluid will still be supplied to chamber 31. However, since both chambers 27 and 28 receive driving fluid the net effect is to maintain the right end of mechanism 70 at the drive pressure and the left side at the exhaust pressure. In other words, the force introduced by the driving fluid in chamber 31 will be offset or canceled by the opposing force presented by the driving fluid in one of chambers 2'7, 28.

During the quarter cycle in which leading mechanism 70 moves to the left from its far right position to its center position shown in full line construction in FIG. 2, during which time mechanism continues its movement to the right to its rightmost position shown in full line construction in FIG. 2, it can be shown that at any given instant liquid in the amount 2 AV will be drawn from the inlet and the same amount will be exhausted to the outlet. More particularly, on the left side of the transformer chambers 37 and 38 together displace in from the primary inlet the amount 2 AV, as those chambers communicate with the inlet through ports 58, 57 and 39 and chamber 31. However, since piston 72 is moving to the left and against the source of driving fluid, chamber 31 in effect discharges driving fluid in the amount AV. Actually, what this means is that 6 AV of the fluid supplied to chambers 37 and 38 will be pushed into those chambers by piston 72. The net amount therefore drawn from the inlet at the left side of the transformer will be 2AV-AV or 1 AV. At the same time, piston 73 will be displacing liquid in the amount AV out of chamber 32 and into the discharge outlet. On the right side of the transformer,

chambers 27 and 28 will be displacing the amount 2 AV from the primary inlet and around the reduced diameter portion 820. Piston 83, however, moving to the right will effectively subtract l AV from the liquid displaced in from the primary inlet so that the net amount drawn will be one AV. Meanwhile, piston 82 will be pumping an amount 1 AV out of chamber 35 and into the primary outlet. Thus, by adding the amounts displaced from the inlet by both the left and right sides and by adding the amounts delivered to the outlet by both sides, it is found that at any given instant the amount 2 AV of liquid refrigerant is displaced in from the primary inlet and the same amount is exhausted at the primary outlet.

When leading mechanism 70 reaches its center position while simultaneously lagging mechanism 80 reaches its extreme right position, the intake and exhaust porting for mechanism 80 will be reversed by mechanism 70, as a consequence of which mechanism 80 reverses its motion and begins to move to the left. Specifically, at the instant mechanism 80 reaches its far right position (shown in full line construction in FIG. 2) full diameter portion 720 blocks port 57 and cuts off the supply of driving fluid to chambers 37 and 38. The liquid flowing into chamber 36 from the primary inlet will now be effective to propel mechanism 8 to the left. As that is taking place, mechanism 70 continues its leftward movement toward its extreme left position (shown in dashed construction in FIG. 2) and this permits chambers 37 and 38 to communicate with the primary outlet through a path which includes ports 58, 57, 44 and 42, chamber 32 and the annular section of chamber 31 surrounding reduced diameter portion 72c. An analysis of the liquid flow into and out of both sides of the transformer, for the one quarter cycle during which mechanism 70 shifts from its center to far left position and lagging mechanism 80 travels from its far right to its center position, will reveal that piston 72 forces an amount AV towards the primary inlet while each of pistons 73, 84 and 85 exhausts an amount AV toward the primary outlet. On the left side there is therefore 1 AV displaced toward the inlet and 3 AV displaced toward the outlet. On the right side, an amount AV flows into each of chambers 27, 28 and 36 from the primary inlet while leftward moving piston 82 effectively robs an amount AV from the primary outlet. On the right, therefore, a total of 3 AV is displaced from the inlet while one AV is taken from the outlet. Combining the flows on both sides, however, it is seen that at any given instant an amount 2 AV is drawn from the primary inlet and an amount 2 66 V is exhausted at the primary outlet.

To complete the analysis of the primary flow circuit, when leading mechanism 70 reaches its far left position and mechanism 80 reaches its center position, mechanism 80 once again reverses the intake and exhaust porting for piston mechanism 70 in order to effectively establish the left and right ends of the cavity of cylinder structure 22 at drive and exhaust pressures, respectively, thereby to reverse the movement of mechanism 70. Specifically, at the instant mechanism 70 reaches its far left position the land provided by full diameter portion 82a blocks port 59 to cutoff the supply of driving fluid to chambers 27 and 28, as a result of which the fluid in chamber 31 (which is at drive pressure) forces mechanism to the right. While this is occurring mechanism 80 is moving leftward from its center position to unblock port 59 so that chambers 27 and 28' will now communicate with the primary outlet via ports 58, 59 and 43. A consideration of the intake and exhaust flow during the one fourth cycle in which mechanism 70 moves from its far left to its center position and mechanism 80 shifts from its center to its far left position, reveals that each of chambers 31 and 36 draws an amount AV from the primary inlet, each of chambers 37, 38, 27, and 28, delivers an amount AV toward the primary outlet, and each of chambers 32 and 35 robs an amount AV from the primary outlet. Adding of the amounts indicates that at any given instant liquid refrigerant in the amount 2 AV is drawn from the primary inlet and the same amount is exhausted at the primary outlet.

The driven fluid (assume that it constitutes a gas) is pumped through the secondary flow circuit by the reciprocating or oscillating action of piston mechanisms 70 and 80. As large pistons 71 and 81 travel within their respective chambers 26 and 34, gas is drawn in at the secondary inlet and discharged at the secondary outlet. The intake and exhaust valving of chamber 26 is controlled by pistons 84 and 85 of piston mechanism 80, while the intake and exhaust porting of chamber 34 is controlled by pistons 74 and of piston mechanism 70. The two cylinder structures are cross valved in the secondary circuit in much the same manner as the cross valving in the primary circuit that causes the reciprocating movement of the eight small pistons. During each stroke of each piston 71, 81 one end of the associated chamber 26, 34 communicates with the secondary outlet while the other end couples to the secondary inlet.

More particularly, during the quarter cycle in which leading mechanism 70 is traveling from its center to its far right position and lagging mechanism is shifting from its far left to its center position (see FIG. 1 gas is fed from the secondary inlet through port 46 and around reduced diameter portion c to supply port 61 and thence to the left end of chamber 26, exhaust port 62 being blocked at that time by full diameter portion 84b. Meanwhile, supply port 63 is closed by full diameter portion 85a but exhaust port 64 will be opened to communicate the right end of that chamber to the secondary outlet over a path comprising port 52 and the annular section of chamber 37 encompassing reduced diameter portion 84d. As a consequence, as piston 71 moves toward its far right position gas from the secondary inlet is drawn into chamber 26 on the left side of piston 71 and is pumped out from the rightside of the piston to the secondary outlet.

Concurrently, pistons 74 and 75 valve chamber 34 in like fashion so that the left end of the chamber is coupled to the secondary inlet and its right side to the secondary outlet. Specifically, supply port 65 is opened by reduced diameter portion 74d and communicates with the secondary inlet via port 48, exhaust port 66 being closed at that time by full diameter portion 75a. Meanwhile, discharge port 68 is opened by reduced diameter portion 750 so that the right end of chamber 34 communicates through port 54 to the secondary outlet, supply port 67 is blocked at that time by full diameter portion 74b.

When mechanism 70 reaches its far right position and begins to return toward its center position mechanism 80 will still be traveling rightward but will have crossed its center position. During that quarter cycle, valving controlled by portions of pistons 84 and 85 reverse the intake and exhaust for chamber 26 in order that the leftward moving piston 71 now pumps gas from.

the left end of chamber 26 into the secondary outlet and draws gas into that chamber at the right end. Particularly, port 62 is opened to the secondary outlet by means of reduced diameter portion 842 and port 51. Port 61 is closed by full diameter portion 85b, port 63 is opened to the secondary inlet via port 47 and the section of chamber 38 surrounding reduced diameter 85c, and port 64 is closed by full diameter portion 84b.

In like manner, when mechanism 80 reaches the end of its rightward moving stroke pistons 74 and 75 reverse the intake and exhaust valving for chamber 34 so that refrigerant gas will now be discharged to the secondary outlet from the left side of chamber 34 and drawn in from the secondary inlet at the right end as piston mechanism 80 travels through its leftward moving stroke.

Assume now that the pressure at the primary inlet is less than that at the primary outlet while at the same time the secondary inlet pressure is greater than the secondary outlet pressure. The fluid in the primary flow circuit will now be unable to provide the necessary power to effect reciprocating movement of each piston mechanism. However since the intake and exhaust valving for the secondary circuit functions in the same manner as that for the primary circuit, the relatively high pressure gas at the secondary inlet serves as the driving or powering fluid to effect reciprocating movement of pistons 71 and 81 and consequently of mechanisms 70 and 80. Hence, the transformer will operate in accordance with its second mode and liquid will be pumped from the primary inlet to the primary outlet in the same way as gas is pumped through the secondary during its first mode of operation.

It will be observed that exhaust ports 62, 64, 66 and 68 are offset from their associated intake ports. By such positioning, as each piston 71, 81 is powered by the secondary fluid to the end of a stroke the piston itself covers the previously open exhaust port thereby providing a bounce chamber for reversing the motion of the associated piston mechanism.

The volumetric flow ratio of the fluids in the primary and secondary circuits is determined by the total volume displaced by the pistons in each of those circuits during the same interval, such as during one complete stroke of either one of the piston mechanisms. Assuming that both circuits are full, the

primary volume displacement would therefore be equal to the total volume of fluid emerging at the primary outlet during the time interval required for mechanism 70, for example, to travel through one complete stroke. Similarly, the secondary volume displacement will equal the total volume of gas discharged at the secondary outlet during one complete stroke of mechanism 70. A characteristic of a fluid transformer is that it tends to maintain a constant volumetric flow ratio between its primary and secondary circuits. In other words, the volume of fluid flowing through one of the flow circuits during a given time interval is directly proportional to the volume of fluid flowing through the other circuit during the same interval and vice versa. In this way, any variation in the flow rate in either one of the flow circuits results in a corresponding flow rate change in the other circuit in accordance with the volumetric flow ratio. As will be seen in the discussion of the refrigeration system of FIG. 3, this is an important characteristic of a fluid transformer.

To explain further, a fluid transformer is somewhat analogous to an electrical transformer which has two isolated but interdependent primary and secondary windings. A voltage applied across the primary winding causes current conduction through that winding and this in turn produces a voltage across, and causes current to flow through, the secondary winding. The pressure differentials across the primary and secondary of a fluid transformer may be likened to the voltages across the primary and secondary of an electrical transformer, and the fluid flow rates are analogous to the currents. The ratio of volumes displaced in the fluid transformer is akin to the turns ratio of an electrical transformer, namely the number of primary winding turns compared to the number of secondary winding turns. Here, however, the analogy must relate the primary-to-secondary turns ratio to the volume displaced in the secondary flow circuit compared to the volume displaced in the primary circuit.

In an electrical transformer the ratio between the voltage applied to the primary and the voltage developed in the secondary is equal to and determined by the turns ratio. On the other hand, the ratio between the primary and secondary current flow is equal to the reciprocal of the turns ratio, or the number of secondary turns relative to the number of primary turns. The ratio between the primary and secondary pressure differentials in a fluid transformer is equal to the ratio between the volume displaced in the secondary relative to that displaced in the primary, and the ratio of the primary flow rate compared to the secondary flow rate equals the ratio of the primary volume displacement versus the secondary volume displacement.

The power in or energy suppled to an electrical transformer with a resistive load is determined by the product of the primary voltage and current and, ignoring losses, must be equal to the power out which is determined by the secondary voltage multiplied by the secondary current. Likewise, in a fluid transformer the power in or delivered to the primary equals the primary pressure differential times the flow rate of the primary fluid and, ignoring losses, that input energy must equal the output energy, namely the product of the secondary pressure differential and the flow rate of the secondary fluid. As is true in both transformer types, any variation of the power out results in a corresponding variation of the power in. For example, if the primary and secondary voltages remain constant in an electrical transformer but the secondary current changes (due to a load variation on the secondary) the primary current must correspondingly change in order for the power input and power output to match. Likewise, in a fluid transformer if the primary and secondary pressure differentials remain unchanged while the secondary flow rate changes in one sense the primary flow rate must vary in the same sense to equalize the input and output energres.

The fluid transformer of FIGS. 1 and 2 may be employed in any system where it is desired to use the fluid in one path to control the fluid in another path. For example, there are a variety of different manners in which applicants unique fluid transformer may be incorporated in a refrigeration system to perform various diverse functions and to accomplish different desired results. One particular application of the invention to a refrigeration system is shown in FIG. 3. There the primary circuit of the fluid transformer (shown in block diagram form and given the reference number 90) is interposed or inserted in a vapor compression refrigeration cycle of an air conditioning system between the outlet of the condenser 92 and the inlet of the evaporator 93.. In this way, the primary is connected in series with the liquid line from the condenser. The secondary flow circuit of the transformer is connected in series with the portion of the compression cycle between the outlet of evaporator 93 and the inlet of condenser 92. Specifically, it is connected in series with the suction line coupling the evaporator to the suction inlet of compressor 94. It will be observed that there is no separate expansion device which is normally included in the vapor compression refrigeration cycle between the outlet of the condenser and the inlet of the evaporator. Since the primary fluid must expand in the primary circuit in order to drive or pump fluid through the secondary, the primary circuit itself serves as the required expansion device for the compression cycle.

Assuming that refrigerant of the R-22 type is used in the system, transformer 90 will be constructed so that its pistons displace a volume in the secondary that is 45 times the volume displaced in the primary. Of course, the primary and secondary circuits have not been so proportioned in the drawings of FIGS. 1 and 2 in order that the primary circuit may be shown in greater detail. A secondary volume displacement that is 45 times the primary volume displacement is desired since an air conditioning system is customarily rated under conditions of 95F dry bulb outdoor air and 67F wet bulb indoor air, and with slightly superheated gaseous refrigerant emerging from the evaporator; and in the presence of those conditions the volume ratio between the gaseous and liquid states of refrigerant R-22 is 45 to l. Stated differently, 1 cubic foot of liquid converts to 45 cubic feet of gas. Hence, with a fluid transformer having a primary displacement 1/45 of its secondary displacement, liquid will be metered or fed to the evaporator at the rate of 1 cubic foot for every 45 cubic feet of suction gas flowing through the secondary to compressor 94', and thus the system is in balance. Under the rated conditions the fluid transformer will have a predetermined operating speed determined by the flow rate of the liquid refrigerant in the primary.

More particularly, refrigerant'gas is received at the compressors suction inlet at a relatively low pressure and temperature and is compressed by the compressor in order to discharge that gas to the inlet of condenser 92 at a relatively high pressure (the high side pressure of the system) and temperature. Heat is removed from the hot discharge gas in the condenser while retaining essentially the same high side pressure. Sufficient heat is deleted to condense the discharge gas so that all of the refrigerant leaves condenser 92 in its liquid state. The liquid refrigerant in passing through the primary circuit of the fluid transformer expands and thus reduces its pressure (to the low side pressure of the system) and temperature, emerging at the primary outlet of the transformer as a mixture of liquid and gas but primarily a liquid. As the mixture then flows through evaporator 93, which is in heat exchange relation or contact with the medium to be cooled, a constant pressure is maintained while heat is transferred from the medium to the refrigerant and the entirety of the refrigerant assumes its gaseous state. Actually, sufficient liquid would be metered to the evaporator to fill it with boiling liquid and thereby maximize the amount of heat that can be absorbed by the refrigerant in the evaporator, while adding a relatively small desired amount of superheat to the refrigerant before it emerges at the evaporators outlet. This superheated gas is returned to the suction inlet of compressor 94 but first passes through the secondary circuit of transformer wherein its pressure increases due to compression work transferred to the secondary as a result of the expansion of the liquid in the primary.

Specifically the expansion of the refrigerant in the expansion engine, constituting the primary, from the high side pressure to the low side pressure provides a pressure differential which in conjunction with the flow rate of the liquid through the primary creates energy which is then used in the secondary circuit to pump and compress the suction gas so that it enters compressor 94 at a pressure higher than it otherwise would. In effect, the transformer provides an additional compression stage. As a consequence, compressor 94 does not have to compress the suction gas all the way from the low side to the high side pressure.

Moreover, by transfering energy from the primary to the secondary an improvement is gained in the performance over conventional systems inasmuch as the evaporator will be fed with a refrigerant having a lower heat content or enthalpy. This advantage is readily appreciated by.referr'ing to the pressure-enthalpy diagram of FIG. 4 which illustrates the operation of the system during high ambient conditions, namely relatively high outdoor temperatures. To digress for a moment, the condenser of an air conditioning system is usually air cooled and is located outside. Since the condensing head pressure is directly proportional to the outside ambient temperature, the pressure of the condensed refrigerant in an all-weather system (one that must provide cooling all year round) will be substantially lower in the winter as compared to its summer level. The pressure-enthalpy diagram thus depends on the ambient conditions. In the high ambient diagram of FIG. 4 the dashed construction lines indicatethe path that is followed by a conventional refrigeration system of the prior art. In transfering PV energy to the secondary, the liquid refrigerant sub-cools and loses heat content in the amount AI-I As shown in FIG. 4, the refrigerant thus arrives at the evaporator with a much lower heat content. This means that more heat can be absorbed by the refrigerant from the medium to be cooled. The initial portion of the compression phase shown in FIG. 4 (starting from the low side pressure) represents the compression introduced in the secondary. That energy is denoted AH and it is, of course, equal to Al-l Assume now that the outdoor temperature suddenly increases above the rated conditions of 95F. The condenser head pressure will rise and this results in a higher discharge pressure at the outlet of the compressor. The pumping capacity of the compressor therefore decreases and this in turn reduces the quantity of gas (in terms of volume per unit of time) that can be removed from the evaporator and delivered through the secondary flow circuit to the compressors inlet. With a slower moving refrigerant in the evaporator more heat will be absorbed per pound circulated, as a consequence of which the refrigerant gas leaves the evaporator at a higher temperature and pressure. The higher pressure creates a lower specific volume (volume per pound) of the suction gas, and the lower the specific volume the lower will be the quantity of gas that will flow through the secondary. At an outdoor temperature of 115F, for example, one cubic foot of liquid refrigerant R-22 converts to only 41 cubic feet of gas, and this does not satisfy the fluid transformers requirement of 45 to 1 thereby causing the system to become unbalanced. In other words, if it is assumed that the outside temperature suddenly climbs from 95F to 115F every cubic foot of liquid passing through the primary creates only 41 cubic feet of gas through the secondary. In effect, there will be a 4 cubic foot void or unused space in the chamber or chambers of the secondary.

In response to the rising outdoor temperature, the transformer automatically reduces its operating speed and stabilizes at a new speed which will re-establish the required 45 to 1 ratio of gas volume versus liquid volume. To elucidate, with less gas to be pumped through the secondary less PV energy need be developed in the primary and transmitted to the secondary to perform the pumping work. With a lower energy requirement to be satisfied by the primary, the liquid flow (volume per unit of time) reduces and the transformer slows down, since its operating speed is directly proportional to the flow rate of the primary fluid. Such a response is consistent with that occurring in an electrical transformer when there is a decrease in the load requirement to be met by the secondary winding. At that time, the secondary current decreases and lowers the output powerpf the transformer. In order for the input power to match the lower power out, the primary current must decrease.

With transformer 90 functioning at a reduced speed and with a smaller quantity of liquid supplied to the evaporator, less heat can be absorbed from the heat load and this causes a drop in both the temperature and pressure of the gas exiting at the evaporators outlet. With a lower pressure, the suction gas volume per pound, or specific volume, increases. This action continues until the ratio of suction gas volume to liquid line volume once again becomes 45 to 1. The net result is that, in response to higher condenser head pressures, the transformer runs slower than at its rated conditions and less pounds per minute of refrigerant are metered through the primary and into the evaporator, starving it in order to restrict the maximum suction pressure to that desirable for the particular compressor used in the system.

It is to be noted that the fluid transformer limits the pressure of the gas delivered to the compressor in much the same way as does a thermostatic expansion valve with the maximum operating pressure feature. However, the transformer will limit the suction pressure to that occurring at the equipment rating point while the thermostatic expansion valve cannot be applied this close to its maximum operating pressure setting.

When the outside temperature drops below the rated conditions, the condenser pressure reduces and the ratio of suction gas volume flow to liquid line flow increases. This is due to increased compressor capacity causing the suction pressure to decrease, thereby developing a higher specific volume of the suction line gas. Assume, for example, that the ambient temperature drops to 60F. At that temperature refrigerant R- 22 has a gas-to-liquid ratio of 52 to l, 1 cubic foot of liquid generating 52 cubic feet of refrigerant gas. Once again the system will be unbalanced but this time there is effectively more gas than the transformers ratio of 45 to l ordinarily allows. Hence, in order to pump the increased volume of gas through the secondary more energy will be needed in the secondary and must be delivered from the primary. The liquid flow in the primary must therefore increase so that the energy demand is satisfied, and this gives rise to an increase in operating speed. With more refrigerant flowing to the evaporator, a portion thereof begins to flood out of the evaporator and through the secondary. The refrigerant in the secondary will now be a mixture of gas and liquid and its specific volume will decrease until the system rebalances under conditions of sufficient liquid flood through to satisfy the transformers requirement of 45 cubic feet of refrigerant flowing through the secondary for every 1 cubic foot of refrigerant in the primary. Thus, in response to a lower outside ambient the transformer settles down or stabilizes at an operating speed faster than that prevailing under the rated conditions. More pounds per minute of refrigerant will be fed to the evaporator and it will be filled at all times with boiling liquid.

It is significant that at outdoor temperatures lower then F the fluid transformer tends to overfeed the evaporator while all other conventional devices such as capillary tubes and expansion valves will underfeed. The liquid overfeed of the fluid transformer is eliminated by a simple control device to be discussed later.

As the refrigeration system has been described thus far, the transformer functions in its mode in which the primary circuit drives the secondary circuit. This occurs so long as the outside ambient remains sufficiently high to hold the condenser head pressure above a predetermined minimum level appropriate to retain a higher pressure at the primary inlet than at the primary outlet. For example, the refrigeration system of FIG. 3 could be designed so that the required pressure differential across the primary circuit would exist at all outdoor temperatures exceeding 25F. At lower ambient temperatures the condensing pressure will be below the required minimum, in which case the pressure at the primary outlet will be greater than that at the primary inlet. The transformer must now function in accordance with its other mode as there is no longer any expanding liquid in the primary to impart energy to the secondary. Furthermore, it is necessary to force or pump the liquid from the lower condensing pressure to the higher pressure at the primary outlet. The fluid transformer automatically switches from one mode to the other anytime the ambient conditions so warrant.

To explain, inasmuch as the condensing pressure during low ambients sets the lowest pressure, the pressure at which evaporation occurs will constitute the highest pressure. The suction gas entering the secondary inlet is thus established at the highest pressure in the system and this permits the transformer to operate in its second mode in which the secondary circuit takes over as the prime mover in the transformer. The nominal primary and secondary circuits thus interchange roles with the secondary now driving the primary. The gaseous refrigerant expands in the secondary and energy is transfered from the secondary to the primary to achieve pumping of the liquid refrigerant from the primary inlet to the outlet.

The operation of the refrigeration system during low ambient conditions is shown by the pressure-enthalpy diagram of FIG. 5. With the condenser pressure below the evaporator pressure, free cooling is obtained as the cycle will be self-sustaining without requiring operation of the compressor. Refrigerant boiled in the evaporator flows through the secondary circuit, expanding to the condenser pressure. The pressure drop in the secondary is denoted AP in FIG. 5. After leaving the secondary the refrigerant flows through the non-running compressor and then through the condenser. The refrigerant is then pumped in the primary to the higher evaporator pressure to complete the cycle. The pressure differential labeled AP indicates the differential through which the liquid refrigerant must be pumped.

Of course, regardless of which flow circuit powers the transformer refrigerant will be automatically metered to the evaporator, by the action of the transformer, to maintain it full of boiling liquid and to produce a suction line to liquid line volume ratio of 45 to 1. For example, if the outside temperature drops to F the gas-to-liquid ratio will normally be 60 to l causing the system to unbalance. At that outdoor temperature the system will operate in accordance with its low ambient mode and the gas in the secondary pumps the liquid through the primary. The over abundance of gas flow in the secondary causes the fluid transformer to increase its speed, as a result of which the liquid flow through the primary to the evaporator increases. Part of the liquid is flooded through into the secondary, the specific volume of the mixture in the secondary decreasing so the system is balanced once again.

The operation of the fluid transformer is also governed and effectively controlled by the amount of evaporator heat loading, the flow rate of the refrigerant in each of the flow circuits varying inversely with that loading in order to properly meter and regulate the refrigerant flow in the vapor compression cycle in response to different heat loads. As the evaporator load increases, more liquid is boiled into gas and additional superheat is added to the gas before it arrives at the evaporators outlet. The suction gas temperature, and consequently its pressure, increase and this results in a decrease of the specific volume of the gas flowing through the secondary circuit. The gas-to-liquid ratio now becomes less than the required 45 to l and the transformers operating speed decreases in the manner previously described, thereby feeding less liquid to the evaporator to bring the evaporator pressure back to a value necessary to provide a gas specific volume of 45 times that of the liquid. Hence, the system does not allow higher than normal or desired suction pressure due to the evaporator heat loading in the same manner as the fluid transformer limits the evaporator pressure in the presence of high condenser head pressures.

On a decreasing evaporator heat load, the suction pressure tends to drop and this increases the specific volume of the suction gas. With the gas-to-liquid ratio now being higher than 45 to l, the fluid transformer increases its speed and overfeeds the evaporator. Sufficient overfeed will occur to return the volume ratio back to 45 to l in the same fashion that takes place under low head pressure conditions. it is thus seen that the transformers operating speed varies inversely with both head pressure and evaporator loading.

In response to compressor shut down, flow in the secondary ceases immediately and the transformer stops running. A blockage is therefore provided in the liquid line and this prevents overfeeding of the evaporator, leaving it comparatively dry. Conventional expansion devices such as capillary tubes continue to feed as long as there is a pressure difference. An expansion valve will overfeed because of its slow response time as a result of which the evaporator will be left reiatively full of refrigerant to satisfy its superheat setting.

As start-up, applicants fluid transformer begins to feed the evaporator immediately. No build-up of the head pressure is necessary to supply the evaporator. Cooling capacity is therefore provided immediately.

As described, under conditions of low head pressure or low evaporator pressure some liquid flood back occurs. To modulate liquid flow in the presence of these conditions, hot discharge gas from the compressor is injected at the primary inlet under the control of a reverse acting thermostatic expansion valve 95. This hot gas occupies some of the displacement in the primary so that while the total volume flow rates are still at the ratio of 45 gas side to 1 liquid side, a portion of the liquid side displacement is spoiled" with the hot discharge gas so that the true ratio of suction gas flow to actual liquid flow can be modulated in an upward direction with increased hot gas. At the rated outside temperature of F no hot gas is required. Preferably, the system would be designed so that 0F outside air a 21) percent overfeed would occur with no control. This means that 25 percent of the desired liquid flow volume would have to be supplied by hot gas. Since under these conditions the volume ratio of hot gas to liquid is approximately 55 to 1, only 0.45 percent (1/55 times 25 percent) of the total flow rate is sacrificed to achieve control. This is insignificant in the overall operation and even though under normal conditions evaporator freeze-up will not take place until the outdoor ambient is below 20F, the small amount of hot gas bypass does provide a slight edge in favor of preventing freezeup.

Reverse acting expansion valve 95 functions in well known manner in response to evaporator superheat, having a valve which opens to an extent inversely proportional to the amount of superheat present in the suction gas. Specifically, there are two controls that combine to set the size of the valve opening. Thermal sensing bulb 96 responds to the suction line temperature and exerts, on one side of a diaphragm in device 95, a force representing that temperature. A pressure sensing tube 97 is in direct communication with the suction line and exerts on the other side of the diaphragm a force proportional to the suction line pressure and this in turn is proportional to the saturation temperature of the refrigerant. The difference between the two forces effectively corresponds to the superheat and provides a net force that determines the size of the valve opening, the greater the superheat the smaller the opening. As evaporator superheat rises, the quantity of hot discharge gas introduced into the liquid flow to the primary inlet decreases, and conversely, decreased superheat results in less gas being added to the liquid at the primary inlet. As a result, the quantity of liquid flow to the evaporator increases on a superheat increase and decreases on a superheat decrease, providing constant evaporator superheat (in the desired amount) under all operating conditions.

Expansion valve 95 is effectively connected across condenser 92, as a consequence of which the pressure drop across the valve equals the condenser pressure drop. The required valve capacity is minimum at high condenser pressures when the condenser pressure drop is also minimum, while the required valve capacity is maximum at low condenser pressures at which time the condenser pressure drop is maximum. This means that the valve has sufficient capacity under all operating conditions to maintain the system under positive control, the system stability thus being exceptional as compared to that obtained in a conventional system where a thermostatic expansion valve directly meters liquid refrigerant.

It is not essential that the secondary volume displacement be 45 times the primary volume displacement. The same results as achieved in the illustrated refrigeration system may also be realized by constructing the fluid transformer of FIGS. 1 and 2 to have a substantially smaller ratio of its secondary volume displacement versus its primary volume displacement. For example, a transformer with a ratio of 15 to 1 could be used. All of the liquid refrigerant from the condenser outlet would flow through the primary circuit but only one-third of the refrigerant gas from the evaporator would be channeled through the secondary. This may easily be done by providing the evaporator with three different branches or coils and by connecting the primary outlet to a distributor having three outlets respectively connected to the inlets of the three branches. The outlets of two of the branches, representing twothirds of the evaporator, are connected directly to the suction inlet of the compressor. The outlet of the other branch coil, constituting the remaining one-third of the evaporator, connects to the secondary inlet of the transformer. The secondary outlet connects to the suction inlet as in FIG. 3. With such an arrangement, liquid will be metered through the distributor to the evaporator on the basis of 1/45 times the volume flow of refrigerant gas received at the suction inlet of the compressor. There is a substantial pressure drop in the distributor so it would serve as part of the expansion device for the compression cycle. The modified system could be constructed so that under high ambient conditions the pressure of the refrigerant would drop from, for example, around 300 psig at the primary inlet to about 120 psig at the primary outlet, a further reduction to around 70 psig taking place in the distributor. The pressure-enthalpy diagrams of FIGS. 4 and 5 would not, of 'course, apply to the modified refrigeration system. A major change in the low ambient diagram is necessary since the liquid would have to be pumped through the primary circuit from the relatively low condenser pressure (for example, around psig) to the pressure psig) required at the inlet of the distributor. In the FIG. 3 system the liquid is pumped in the primary, during low ambients, over a muchsmaller pressure differential.

As mentioned, there are many different ways applicants fluid transformer may be incorporated in a refrigeration system to achieve a variety of advantageous results. As another example, the transformer can be used in the refrigeration system of the well known type wherein the evaporator is overfed into an accumulator and the overfeed is recirculated through the evaporator by means of an electrically powered pump. This improves the heat transfer property of the evaporator to maximize the heat absorbed from the load. The pump could be replaced by the fluid transformer, the driving power being supplied by the refrigerant gas. The transformer also finds many uses in other than refrigeration system. For example, it could serve as a boiler feed water pump using steam as the powering medium. Of course the novel fluid-powered expansion engine itself, which forms part of the transformer, may perform many different functions. It is capable of driving a variety of different loads other than pumps.

Applicant has therefore provided a unique fluidpowered expansion engine which features a pair of double-acting, cross coupled piston systems each controlling the intake and exhaust portion for the other.

Certain features described in the present application are disclosed and claimed in copending application Ser. No. 115,506, filed concurrently herewith in the name of the present applicant, and assigned to the present assignee.

While a particular embodiment of the invention has been shown and described, modifications may be made, and it is intended in the appended claims to cover all such modifications as may fall within the true spirit and scope of the invention.

I claim:

1. A fluid-powered expansion engine driven by driving fluid received at an inlet at a predetermined drive pressure and discharged at an outlet at a lower exhaust pressure, comprising:

first and second cylinder structures respectively having first and second cavities each of which includes at least one cylindrical chamber;

first and second free piston mechanisms respectively movable through said first and second cavities and constituting the only two moving parts in the expansion engine;

means including at least a portion of said second piston mechanism for directly providing intake and exhaust valving of said first cavity to effect, in response to the driving fluid, double acting reciprocating movement of said first piston mechanism through a two-stroke cycle;

and means including at least a portion of said first piston mechanism for directly providing intake and exhaust valving of said second cavity to effect, in response to the driving fluid, double acting reciprocating movement of said second piston mechanism through a two-stroke cycle.

2. A fluid-powered expansion engine according to claim 1 in which each of said piston mechanisms travels at substantially the same speed in completing each cycle of operation, said second piston mechanism being one-fourth of a cycle out of phase with respect to, and lagging, said first piston mechanism.

3. A fluid-powered expansion engine according to claim 1 in which the driving fluid is supplied from the inlet to one side of each piston mechanism, during one of its two strokes, to establish that side at drive pressure while its other side is established at exhaust pressure and delivers the driving fluid to the outlet, and in which the pressures on the two sides are reversed during its other stroke, the driving fluid being received at said other side and discharged from said one side, and in which each piston mechanism travels at a speed that varies directly with the flow rate of the driving fluid from the inlet to the outlet.

4. A fluid-powered expansion engine according to claim 1 in which two portions of said first cavity are alternately coupled to the inlet and outlet, to alternately establish those portions at drive and exhaust pressures, by valving controlled by said second piston mechanism, and in which two sections of said second cavity are alternately coupled to the inlet and outlet, to alternately establish those sections at drive and exhaust pressures, by valving controlled by said first piston mechanism.

5. A fluid-powered expansion engine according to claim 1 in which each of said cylinder structures is coupled to both the inlet and outlet, and in which different sections of each of said cavities are ported and interconnected to different sections of the other cavity, the interconnections being alternately opened and closed by portions of said piston mechanisms as said mechanisms cyclically move through said cavities.

6. A fluid-powered expansion engine according to claim 5 in which each of said piston mechanisms has a plurality of cylindrical pistons divided into full diameter and reduced diameter portions, and in which said interconnections are closed by the full diameter portions of said pistons and opened by the reduced diameter portions.

7. A fluid-powered expansion engine according to claim 1 in which the driving fluid is in its liquid state.

8. A fluid-powered expansion engine according to claim 1 in which the driving fluid is in its gaseous state.

9. A fluid-powered expansion engine according to claim 1 in which said piston mechanisms are similarly shaped, wherein each of said cavities effectively includes a plurality of cylindrical chambers having parallel axes, and in which each of said piston mechanisms includes a corresponding plurality of pistons each of which reciprocally moves through a respective one of the chambers.

10. A fluid-powered expansion engine according to claim 9 in which the driving fluid for propelling said first piston mechanism is supplied from the inlet to said first cavity via one of the chambers of said second cavity and through valving controlled by one of the pistons of said second piston mechanism, in which the driving fluid is discharged from said first cavity by way of another chamber of said second cavity and through valving controlled by another one of the pistons of said second piston mechanism, wherein the driving fluid for powering said second piston mechanism is delivered from the inlet to said second cavity via one of the chambers of said first cavity and through valving controlled by one of the pistons of said first piston mechanism, and in which the driving fluid is discharged from said second cavity via another chamber of said first cavity and through valving controlled by another one of the pistons of said first piston mechanism.

11. A fluid-powered expansion engine according to claim 10 in which the valving of the driving fluid supplied to said first cavity is effected by reduced and full diameter portions of said one piston of said second piston mechanism, in which the valving of the driving fluid discharged from said first cavity is achieved by reduced and full diameter portions of said other piston of said second piston mechanism, wherein the valving of the driving fluid supplied to the second cavity is effected by reduced and full diameter portions of said one piston of said first piston mechanism, and in which the valving of the driving fluid discharged from said second cavity is achieved by reduced and full diameter portions of said other piston of said first piston mechanism.

12. A fluid-powered expansion engine according to claim 1 in which each of said cavities is cross-valved to the other and communicated to both the inlet and outlet, portions of said piston mechanisms serving as movable valve members in order to apply drive pressure to one side of each of said piston mechanisms dur- 'ing one of its strokes and to apply drive pressure to the other side of each piston mechanism during its other stroke.

13. A fluid-powered expansion engine according to claim 1 in which each cavity communicates with the outlet while its associated piston mechanism moves through each stroke, thereby to discharge the driving fluid to the outlet, and in which the communication to the outlet is blocked at the very end of each stroke to provide a bounce chamber for reversing the motion of the piston mechanism.

14. A fluid-powered expansion engine/fluid pump arrangement comprising:

a source of driving fluid; a source of driven fluid; first and second cylinder structures respectively having first and second cavities each of which includes a plurality of cylindrical chambers;

first and second free piston mechanisms respectively movable through said first and second cavities and constituting the only two moving parts in the arrangement;

means including at least a portion of said second piston mechanism for directly providing intake and exhaust valving of said first cavity to effect, in response to said driving fluid, double acting reciprocating movement of said first piston mechanism through a two-stroke cycle;

means including at least a portion of said first piston mechanism for directly providing intake and exhaust valving of said second cavity to effect, in response to said driving fluid, double acting reciprocating movement of said second piston mechanism through a two-stroke cycle;

and a pump, driven by said first and second piston mechanisms, for pumping said driven fluid.

15. A fluid-powered expansion engine/fluid pump arrangement according to claim 14 in which said pump includes first and second double acting pump pistons each of which forms part of a respective one of said first and second piston mechanisms, said first pump piston moving back and forth in one of the chambers of said first cavity and said second pump piston moving back and forth in one of the chambers of said second cavity.

16. A fluid-powered expansion engine/fluid pump arrangement according to claim 15 in which said driven fluid is supplied to and discharged from said one chamber of said first cavity by valving controlled by portions of said second piston mechanism, and in which said driven fluid is supplied to an exhausted from said one chamber of said second cavity by valving controlled by portions of said first piston mechanism.

17. A fluid transformer for utilizing a driving fluid, received at a primary inlet and discharged at a primary outlet, to pump a driven fluid from a secondary inlet to a secondary outlet, comprising:

first and second cylinder structures respectively having first and second cavities each of which includes a plurality of cylindrical chambers;

first and second free piston mechanisms respectively movable through said first and second cavities and constituting the only two moving parts in the fluid transformer;

means for providing a primary flow circuit for the driving fluid from the primary inlet to the primary outlet and including at least one chamber of said first cavity and at least one chamber of said second cavity;

means for providing a secondary flow circuit for the driven fluid from the secondary inlet to the secondary outlet and including at least one chamber of said first cavity and at least one chamber of said second cavity;

and valving means including portions of said first and second piston mechanisms for directly providing intake and exhaust valving of said first and second cavities to effect, in response to the driving fluid, double acting reciprocating movement of each of said piston mechanisms through a two-stroke cycle, thereby resulting in pumping of the driven fluid through said secondary flow circuit.

18. A fluid transformer according to claim 17 in which the ratio of the quantities of fluid flowing through said primary and secondary flow circuits is determined by the ratio of the volumes displaced by said piston mechanisms in said flow circuits during one stroke of one of said piston mechanisms, any flow change in one of said circuits resulting in a corresponding change in the other circuit in accordance with that ratio.

19. A fluid transformer according to claim 17 in which said primary and secondary flow circuits are interchangable in that the driving fluid may be supplied to said secondary flow circuit to cause pumping of the driven fluid through said primary circuit. 

1. A fluid-powered expansion engine driven by driving fluid received at an inlet at a predetermined drive pressure and discharged at an outlet at a lower exhaust pressure, comprising: first and second cylinder structures respectively having first and second cavities each of which includes at least one cylindrical chamber; first and second free piston mechanisms respectively movable through said first and second cavities and constituting the only two moving parts in the expansion engine; means including at least a portion of said second piston mechanism for directly providing intake and exhaust valving of said first cavity to effect, in response to the driving fluid, double acting reciprocating movement of said first piston mechanism through a two-stroke cycle; and means including at least a portion of said first piston mechanism for directly providing intake and exhaust valving of said second cavity to effect, in response to the driving fluid, double acting reciprocating movement of said second piston mechanism through a two-stroke cycle.
 2. A fluid-powered expansion engine according to claim 1 in which each of said piston mechanisms travels at substantially the same speed in completing each cycle of operation, said second piston mechanism being one-fourth of a cycle out Of phase with respect to, and lagging, said first piston mechanism.
 3. A fluid-powered expansion engine according to claim 1 in which the driving fluid is supplied from the inlet to one side of each piston mechanism, during one of its two strokes, to establish that side at drive pressure while its other side is established at exhaust pressure and delivers the driving fluid to the outlet, and in which the pressures on the two sides are reversed during its other stroke, the driving fluid being received at said other side and discharged from said one side, and in which each piston mechanism travels at a speed that varies directly with the flow rate of the driving fluid from the inlet to the outlet.
 4. A fluid-powered expansion engine according to claim 1 in which two portions of said first cavity are alternately coupled to the inlet and outlet, to alternately establish those portions at drive and exhaust pressures, by valving controlled by said second piston mechanism, and in which two sections of said second cavity are alternately coupled to the inlet and outlet, to alternately establish those sections at drive and exhaust pressures, by valving controlled by said first piston mechanism.
 5. A fluid-powered expansion engine according to claim 1 in which each of said cylinder structures is coupled to both the inlet and outlet, and in which different sections of each of said cavities are ported and interconnected to different sections of the other cavity, the interconnections being alternately opened and closed by portions of said piston mechanisms as said mechanisms cyclically move through said cavities.
 6. A fluid-powered expansion engine according to claim 5 in which each of said piston mechanisms has a plurality of cylindrical pistons divided into full diameter and reduced diameter portions, and in which said interconnections are closed by the full diameter portions of said pistons and opened by the reduced diameter portions.
 7. A fluid-powered expansion engine according to claim 1 in which the driving fluid is in its liquid state.
 8. A fluid-powered expansion engine according to claim 1 in which the driving fluid is in its gaseous state.
 9. A fluid-powered expansion engine according to claim 1 in which said piston mechanisms are similarly shaped, wherein each of said cavities effectively includes a plurality of cylindrical chambers having parallel axes, and in which each of said piston mechanisms includes a corresponding plurality of pistons each of which reciprocally moves through a respective one of the chambers.
 10. A fluid-powered expansion engine according to claim 9 in which the driving fluid for propelling said first piston mechanism is supplied from the inlet to said first cavity via one of the chambers of said second cavity and through valving controlled by one of the pistons of said second piston mechanism, in which the driving fluid is discharged from said first cavity by way of another chamber of said second cavity and through valving controlled by another one of the pistons of said second piston mechanism, wherein the driving fluid for powering said second piston mechanism is delivered from the inlet to said second cavity via one of the chambers of said first cavity and through valving controlled by one of the pistons of said first piston mechanism, and in which the driving fluid is discharged from said second cavity via another chamber of said first cavity and through valving controlled by another one of the pistons of said first piston mechanism.
 11. A fluid-powered expansion engine according to claim 10 in which the valving of the driving fluid supplied to said first cavity is effected by reduced and full diameter portions of said one piston of said second piston mechanism, in which the valving of the driving fluid discharged from said first cavity is achieved by reduced and full diameter portions of said other piston of said second piston mechanism, wherein the valving of the driving fluid supplied to the second cavity is effected bY reduced and full diameter portions of said one piston of said first piston mechanism, and in which the valving of the driving fluid discharged from said second cavity is achieved by reduced and full diameter portions of said other piston of said first piston mechanism.
 12. A fluid-powered expansion engine according to claim 1 in which each of said cavities is cross-valved to the other and communicated to both the inlet and outlet, portions of said piston mechanisms serving as movable valve members in order to apply drive pressure to one side of each of said piston mechanisms during one of its strokes and to apply drive pressure to the other side of each piston mechanism during its other stroke.
 13. A fluid-powered expansion engine according to claim 1 in which each cavity communicates with the outlet while its associated piston mechanism moves through each stroke, thereby to discharge the driving fluid to the outlet, and in which the communication to the outlet is blocked at the very end of each stroke to provide a bounce chamber for reversing the motion of the piston mechanism.
 14. A fluid-powered expansion engine/fluid pump arrangement comprising: a source of driving fluid; a source of driven fluid; first and second cylinder structures respectively having first and second cavities each of which includes a plurality of cylindrical chambers; first and second free piston mechanisms respectively movable through said first and second cavities and constituting the only two moving parts in the arrangement; means including at least a portion of said second piston mechanism for directly providing intake and exhaust valving of said first cavity to effect, in response to said driving fluid, double acting reciprocating movement of said first piston mechanism through a two-stroke cycle; means including at least a portion of said first piston mechanism for directly providing intake and exhaust valving of said second cavity to effect, in response to said driving fluid, double acting reciprocating movement of said second piston mechanism through a two-stroke cycle; and a pump, driven by said first and second piston mechanisms, for pumping said driven fluid.
 15. A fluid-powered expansion engine/fluid pump arrangement according to claim 14 in which said pump includes first and second double acting pump pistons each of which forms part of a respective one of said first and second piston mechanisms, said first pump piston moving back and forth in one of the chambers of said first cavity and said second pump piston moving back and forth in one of the chambers of said second cavity.
 16. A fluid-powered expansion engine/fluid pump arrangement according to claim 15 in which said driven fluid is supplied to and discharged from said one chamber of said first cavity by valving controlled by portions of said second piston mechanism, and in which said driven fluid is supplied to an exhausted from said one chamber of said second cavity by valving controlled by portions of said first piston mechanism.
 17. A fluid transformer for utilizing a driving fluid, received at a primary inlet and discharged at a primary outlet, to pump a driven fluid from a secondary inlet to a secondary outlet, comprising: first and second cylinder structures respectively having first and second cavities each of which includes a plurality of cylindrical chambers; first and second free piston mechanisms respectively movable through said first and second cavities and constituting the only two moving parts in the fluid transformer; means for providing a primary flow circuit for the driving fluid from the primary inlet to the primary outlet and including at least one chamber of said first cavity and at least one chamber of said second cavity; means for providing a secondary flow circuit for the driven fluid from the secondary inlet to the secondary outlet and including at least one chamber of said first cavity and at least one chamber of said second cavity; and valving means including portions of said first and second piston mechanisms for directly providing intake and exhaust valving of said first and second cavities to effect, in response to the driving fluid, double acting reciprocating movement of each of said piston mechanisms through a two-stroke cycle, thereby resulting in pumping of the driven fluid through said secondary flow circuit.
 18. A fluid transformer according to claim 17 in which the ratio of the quantities of fluid flowing through said primary and secondary flow circuits is determined by the ratio of the volumes displaced by said piston mechanisms in said flow circuits during one stroke of one of said piston mechanisms, any flow change in one of said circuits resulting in a corresponding change in the other circuit in accordance with that ratio.
 19. A fluid transformer according to claim 17 in which said primary and secondary flow circuits are interchangable in that the driving fluid may be supplied to said secondary flow circuit to cause pumping of the driven fluid through said primary circuit. 